1. Field of the Invention
The field of the invention relates to semiconductor chips and in particular to providing input/output interface devices for these semiconductor chips.
2. Description of the Prior Art
In typical semiconductor fabrication techniques, data handling cores or chips are fabricated with data handling logic circuitry such as processing logic or data storage within them. These chips are built up in large numbers on a single wafer of semiconductor material, typically silicon. In order to provide power and data access to the chips, the individual chips are patterned with small connection or bonding pads. These are pads of conductive material such as metal and are generally arranged near the edge of the chips to make external access to these pads easier.
The chips are cut out of the wafer and mounted in packaging and wires are typically bonded to the bonding pads to allow signals and power to be transmitted to and from the chips. These bonding pads connect to the chip via input/output devices that provide some handling and control of the power and signals that are received and transmitted. The wires lead to pins on the outside of the packaging, which are attached to the rest of the circuitry making up the electronic system.
As chips become more complex, more and more input/output devices are required to handle the power and data signals transmitted to and from the chip.
In order to provide a compact easily built system these input/output devices are generally designed to abut each other and to have the same length. In this way they are aligned with each other so that power rails can be built across a row of input/output devices and each input/output device can be connected to any one of the rails as required. The length of an input/output device is the dimension of the device that is perpendicular to an external edge of the chip that the device is sitting adjacent to. It is also advantageous if these input/output devices all have the same width as this makes it easier when arranging the wires between the bonding pads and the external pins on the packaging, as these pins are generally arranged in a set pattern.
The input/output devices are therefore designed to be the same size and this is the size of the largest input/output device required. As the size of a chip is limited the increasing number of input/output devices required in increasingly complex systems along with these devices all being the same size and being arranged close to an edge of the chip leads to a problem of restricted space available for mounting of the input/output devices.
In some techniques the input/output devices have been designed to be narrower and correspondingly longer so that more input/output devices can be fitted alongside each other on the outer edge of the chip. However, a drawback of this is that the bonding area required to bond a wire to the input/output device is then wider than the input/output device itself, so that these bonding pads cannot be aligned with each other. This arrangement is termed a staggered arrangement and this leads to a difference in length of the bonding wires which can introduce skew into the system.
It would be desirable to provide a system with an increased number of input/output devices while not unduly increasing skew into the system.